The Effects Of Growth Of Leymus Chinensis(Trin.)Tzvel.on Soil Hydrolase Activities And Enzyme Stoichiometry Of Different Successional Stages In Songnen Grassland

The invasion and colonization of pioneer species can change the composition,structure,even succession process of plant community.Different successional stages have their dominant species and maintain them for a period of time.Soil enzymes are an essential part of the interaction between plants and soil microorganisms.Their activities are one of the indicators of soil function.Soil enzyme stoichiometry is often used to reflect soil microbial metabolism and nutrient constraint.However,at present,the conditioning effects of colonization of pioneer or dominant species on soil enzyme activities and enzyme stoichiometry in different successional stages are still poorly understood.Leymus chinensis(Trin.)Tzvel.is an important plant component and even the dominant species in the middle and late recovery successional stages of Songnen salinized grassland.In this study,four successional stages of the "alkali spot-L.chinensis community" successional series in Songnen Plateau were selected,namely severely degraded(ED),moderately degraded(MD),lightly degraded(LD)and non-degraded stage(ND).To study the influence of successional stage,growth of L.chinensis and their interaction on soil hydrolase activities and enzyme stoichiometry,the soil samples taken from each successional stage were conditioned by L.chinensis and compared with the soil samples under pre-conditioning by L.chinensis.Seven soil hydrolase activities were determined,including C-,N-and P-degrading enzymes,i.e.,?-1,4-glucosidase(?G),?-1,4-glucosidase(?G),?-1,4-xylosidase(?X),cellobiohydrolase(CBH),?-1,4-N-acetylglucosaminidase(NAG),L-leucine aminopeptidase(LAP)and acid phosphatase(a P).Besides,soil physicochemical parameters and microbial biomass carbon were measured.The main conclusions are as follows:(1)C-degrading enzymes activities(?G,?G,?X and CBH)and NAG activities showed a gradually increasing trend with the recovery succession process of Songnen degraded grassland.However,the activities of LAP and a P showed a decreasing trend.Except for NAG,the growth of L.chinensis had significant(P<0.05)effects on other hydrolase activities,and these effects were dependent on successional stages.In addition to LAP,L.chinensis cultivation significantly changed the distribution patterns(i.e.,relative proportions)of other hydrolase activities at different successional stages.(2)The soil enzyme stoichiometry showed that the soil microorganisms in the successional series of Songnen degraded grassland were all restricted by the P element,but this constraint was gradually alleviated with the recovery succession process of grassland.The growth of L.chinensis significantly alleviated the soil microbial P limitation in SD and MD but significantly intensified P limitation in LD.(3)Soil pH,EC,TC,TN,AN,AP,MBC and soil nutrient stoichiometry were significant(P<0.05)or extremely significant(P<0.01)different among different successional stages.The growth of L.chinensis significantly influenced soil EC,SWC,TC,TP,AN,MBC,TC:TN and TN:TP.(4)The key soil parameters affecting soil hydrolase activities were soil p H,SWC and the availability of C,N and P elements.The key factors affecting soil enzyme stoichiometry were soil p H,EC,MBC,C,N,P content and their stoichiometric ratio.However,the key soil factors affecting soil hydrolase activities and enzyme stoichiometry changed under pre-and post-conditioning by L.chinensis.In summary,the growth of L.chinensis significantly changed the soil hydrolase activities and enzyme stoichiometry in the severely,moderately,lightly and non degraded stage of the "alkali spot-L.chinensis community" successional series in Songnen grassland.Improving soil nutrient availability is the primary way that L.chinensis affects soil hydrolase activities and enzyme stoichiometry in different successional stages.The results of this study suggest that L.chinensis,which invades and colonizes in the middle and late stages of recovery succession of Songnen salinized grassland,promotes the restoration of soil function by changing the soil nutrient availability and hydrolase activity patterns.Meanwhile,this study also proves that soil enzyme stoichiometry(C:N:P)can be used as an effective index to monitor the restoration status of Songnen degraded grassland.This study is of crucial theoretical significance to reveal the role and mechanism of dominant plant species on reshaping soil function in degraded grassland recovery.